OceanBrowser

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OceanBrowser allows to visualize gridded fields on-line. It is used in SeaDataNet (http://gher-diva.phys.ulg.ac.be/web-vis/), chemical data in EMODNET (http://gher-diva.phys.ulg.ac.be/emodnet/) and for data set product by the GHER (http://gher-diva.phys.ulg.ac.be/gher-data/).

Within the SeaDataNet and EMODNET (Chemical lot) projects, several national ocean data centers have created gridded climatologies of different ocean properties using the data analysis software DIVA. In order to give a common viewing service to those interpolated products, the GHER has developed OceanBrowser which is based on open standards from the Open Geospatial Consortium (OGC), in particular Web Map Service (WMS) and Web Feature Service (WFS). These standards define a protocol for describing, requesting and querying two-dimensional maps at a given depth and time.

Contents

Features

OceanBrowser currently supports the following operations:

  • Horizontal sections of the 4-dimensional fields (longitude, latitude, depth and time) can be visualized at a selected depth and time. The climatological fields can also be interpolated and visualized on arbitrary vertical sections (Figure 1).
  • The maps displayed in the browser are created dynamically and therefore several options are made available to the user to customize the graphical rending of those layers. Layers can be displayed either using interpolated shading, filled contours or simple contours and several options controlling the color-map are also available.
  • The horizontal and vertical sections can be animated in order to study the evolution in time.
  • Image can be saved in raster format (PNG) and vector image formats (SVG, EPS, PDF). It can also be saved as a KML file so that the current layer can be visualized in programs like Google Earth and it can be combined with other information imported in such programs.
  • The underlying 4-dimensional NetCDF file can be either downloaded as a whole from the interface or only as a subset using the linked OPeNDAP server.
  • The web interface can also import third-party layers by using standard WMS requests. The user needs only to specify the URL of the WMS server and its supported version.


Usage

  • Select a domain and variable in the "Add layer/Select data product" dialog. Under the variable name, the variable with two error thresholds (0.3 and 0.5) can be chosen. In "additional fields" the full field without error thresholds are available as well as data distribution (Logarithm10 of number of data in bins), outliers distribution (Logarithm10 of number of outliers data in bins), relative error and the near bottom value (deepest value). A "data bin" is a grid cell of the interpolated grid.
  • To remove a field from the map, click on the cross (close.png) next to the color bar (on the right).

File:OceanBrowser_select_data_product.png

  • Several data sets can be visualized at the same time. For example, ocean temperature from the North Sea, Atlantic Ocean and Mediterranean Sea can be visualized at the same time. The consistency of the several ocean products in adjacent regions can be easily assessed and potential problems can be highlighted (Figure 1). This feature is available for horizontal as well for as for vertical sections. By choosing simple contours of one field in combination with filled contours of other field one visually sees the correspondence or location of frontal structures.

Change style

The appearance of the field can be customized by clicking on the style button (config.png) where you can range color map, color range, plot style (flat shading, contours and filled contours).

Style dialog‎

Icons

  • zoom-plus-mini.png: zoom in
  • zoom-minus-mini.png: zoom out
  • zoom-world-mini.png: reset zoom
  • north-mini.png, east-mini.png, south-mini.png, west-mini.png: move to North, East, South or West
  • include-all-layers.png: Change zoom level to include all layers
  • panning-hand-on.png, panning-hand-off.png: panning mode is enabled (default) or disabled
  • drag-rectangle-on.png, drag-rectangle-off.png: zoom by drawing a rectangle is enabled or disabled (default). Click to draw a first corner of the rectangle and then drag it to the desired size.

Horizontal Sections

Per default the surface layer and the first time slice is shown. This can be changed in the depth and time select boxes next to the color bar (on the right). After the choice is confirmed by clicking on 'Update', the map is redrawn.

Vertical section

  • Vertical sections can be extracted by selecting the corresponding tab on the upper left.
  • The overview map shows the same time instance and depth levels as the horizontal view (which is the the first time instance of the surface layer per default).
  • With a mouse a section can be draw in the overview map. A simple click starts a section or adds a point and double-click finishes it.
  • After a section is finished it will appear, the field will be interpolated onto the requested section and drawn in the central part (labeled "vertical section" in the figure below). The coordinates of this plots are distance in arc degrees from the starting point (1 arc degree is always equal to 1 degree in the North-South direction and approximately 111 km) and depth (0 is the surface and value are negative in water).

Instead of drawing a section by the mouse, one can generate a section based on a fixed distance from coast or depth. The corresponding option has be chosen in "Interaction mode". The work-flow is illustrated in the following figure. As multiple disconnected line segments are at a fixed distance form coast (or constant ocean depth). One has the select by the mouse in the overview map the desired section.

Downloading data products

You can open the download dialog by clicking on the download icon (download.png) next to the color bar. You can either download the data (netCDF or OPeNDAP) or download images for the current layer.

Data products

Data products can be downloaded as NetCDF files by using the button labeled "Download NetCDF". A NetCDF file will contain the DIVA analysis for a single parameter as well as meta data as NetCDF attributes. User can also download subset of the data products by using the button "OPeNDAP Service". By click this button, a new window will open with the attributes of the NetCDF file. The URL of this window need to be copied into your OPeNDAP application.


File:OceanBrowser_download.png

Useful software to access the data in netCDF/OPeNDAP are:

ncBrowse
A Graphical netCDF File Browser
Panoply
netCDF, HDF and GRIB Data Viewer
Ncview
a netCDF visual browser

Images

It is also possible to download the current view as an image file by specifying the width and height of the image and the longitude and latitude range.

Future outlook

The upcoming HTML5 standard brings a large range of new features to modern web browsers which will also be useful to visualize ocean data. WebGL is a technology which allows displaying 3 dimensional data in a web browser using hardware acceleration. An experimental JavaScript library, called EarthGL (figure 2), has been developed which allows displaying horizontal and vertical sections of ocean fields on a globe with realistic topography. This JavaScript library is strongly inspired by OpenLayers and should be familiar to developers using the library. WebGL is implemented by the current version of all major browsers as long as the graphics drivers supports WebGL.

Additional information

For partners of the SeaDataNet and EMODNET Chemistry, description about importing data has been written.

Feedback

Question and comments can be addressed to Alexander Barth (a dot barth at ulg dot ac dot be)

Acknowledgements

Funding was provided by SeaDataNet (FP7) and Emodnet Chemistry (DG-MARE).

GEBCO project is acknowledged for providing the GEBCO world map, http://www.gebco.net/

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